This invention relates to a referencing or alignment system for properly positioning an external lens system in accurate alignment with the geometric center of an inside lens element, and more particularly to method and apparatus for accurately locating a projection lens system externally of a cathode ray tube (CRT), such as a TV tube, with the geometric center of a lens element formed on the inside surface of the panel of the TV tube, while such tube is sealed and under vacuum.
It is contemplated that the next generation of cathode ray tubes for projection TV will have a lens element located on the inside surface of the CRT panel face. Such lens element will become an integral part of the total projection TV lens system utilized in such projection TV. Thus, it is contemplated in the pressing of the panel, to form a spherical or aspherical lens on the inside surface of the panel simultaneously with the pressing of the panel per se. The tube which is formed with the panel lens is processed through the normal tube making operations including the screening, aluminizing, frit sealing, gun insertion, and exhaust procedures utilized in normal tube making processes.
After the TV bulb with the lens element is made into a projection TV tube, a problem arises as to how to align the lens on the inside of the evacuated tube with an external projection TV lens system. That is, to effectively utilize the lens that is molded into the inside surface of the panel, the lens itself must be accurately aligned with the external projection lens system. This has presented a problem to the set manufacturers, since after the tube is made, there is no longer access to the inside lens surface since the tube is exhausted and sealed, and therefore an external alignment with the internal lens is not an easy situation. Although an optical laser alignment or other system could possibly be established externally of the tube, such a system would not only be complex and involve numerous alignment steps but also would incur undue expense.
U.S. Pat. No. 4,150,320 discloses an integral lens cathode ray tube system wherein a curved glass panel is disposed, by means of an optical resin material, in a manner related to the viewing portion of the cathode ray tube, such that an exterior double concave or convexal concave lens is provided. U.S. Pat. No. 4,387,404 sets forth a projection television tube alignment means and method, and points out the fact that precision aligning of the projection tubes is essential in projection television systems. U.S. Pat. No. 4,672,458 relates to a projection television system and shows the complexity of the conventional system of externally mounted lenses.
In order to overcome the alignment problems associated with an internal lens and an external projection system, it is an object of the present invention to provide an external system for locating the geometric center of a lens element located on the inside of an enclosure, such as the panel of a projection TV CRT, such that the CRT can be assembled into an accurately aligned system composed of the internal CRT lens element and an external projection TV lens system.